Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters
Reexamination Certificate
1998-08-28
2001-02-13
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Lumped type parameters
Reexamination Certificate
active
06188229
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a conductive-pattern recognition apparatus and more particularly, to conductive-pattern recognition apparatus for recognizing a conductive pattern formed on a substrate, which is applicable to automatic pattern inspection of Printed Wiring Boards (PWBs) or the like.
2. Description of the Prior Art
In recent years, automation in the fabrication processes of PWBs has been progressing more and more for the purpose of labor-saving andefficiency-raising. According to this tendency, various inspection procedures such as visual inspection and production-lot discrimination, which were performed manually, have been becoming automated.
For example, various conductive-pattern recognition apparatuses making it possible to perform automatically the pattern inspection procedures of PWBs have been developed and practically used.
An example of the conventional conductive-pattern recognition apparatuses is shown in
FIG. 1
, which recognizes optically the conductive patterns of PWBS.
As shown in
FIG. 1
, this conventional conductive-pattern recognition apparatus is comprised of a moving or translation mechanism
106
for moving or translating a PWB
109
to be inspected in a direction A, a strip-shaped light source
130
for illuminating the surface of the PWB
109
with light, a lens
131
for collecting the light reflected by the surface of the PWB
109
, and an optical line sensor
132
for sensing the light reflected by the surface of the PWB
109
and collected by the lens
131
. The surface of the PWB
109
is covered with an insulator
133
except for a conductive circuit pattern
110
. The optical line sensor
132
, which has Charge-Coupled Devices (CCDs) arranged along a straight line, is fixed in parallel to the light source
130
and the lens
131
.
On recognition or operation of this apparatus, the PWB
109
with the conductive pattern
110
is translated by the translation mechanism
106
in the direction A perpendicular to the line sensor
132
. The light emitted from the light source
130
is reflected by the surface of the PWB
109
and then, the reflected light is collected by the lens
131
to be inputted into the line sensor
132
.
The intensity of the reflected light by the conductive pattern
110
is higher than that of the reflected light by the insulator
133
. Therefore, the conductive pattern
110
is able to be recognized by detecting the intensity difference of the reflected light.
In addition to the optical recognition apparatus explained above, pressure-sensitive recognition apparatuses have been known. An example of these conventional pressure-sensitive recognition apparatuses is shown in
FIG. 2
, which is an embossed-character reader and is disclosed in the Japanese Non-Examined Patent Publication No. 2-257380 published in 1990.
The conventional embossed-character reader is comprised of an idler roller
206
for moving or translating an embossed card
234
(i.e., a specimen) on which embossed characters
235
are formed, a pressure-sensitive rubber roller
236
whose electric resistance varies according to an applied pressure, a rotary encoder
237
fixed to the axis of the pressure-sensitive rubber roller
236
for detecting the rotational amount or distance of the roller
236
, and a resistance detection means (not shown) for detecting the electric resistance of the pressure-sensitive rubber roller
236
.
The pressure-sensitive rubber roller
236
has a pressure-sensitive rubber sheet formed by a silicone rubber containing proper conductive particles uniformly dispersed therein. The pressure-sensitive rubber sheet has electrodes S
11
, S
12
, S
13
, and S
14
at its four sides.
In the conventional embossed-character reader shown in
FIG. 2
, the specimen or embossed card
234
is translated in the direction A between the rollers
206
and
236
on reading operation. During the reading operation, the electric resistance of the pressure-sensitive rubber sheet of the roller
236
and the rotational distance of the roller
236
are detected, thereby obtaining a pattern of the area change due to the embossed characters
235
. Then, the pattern of the area change thus obtained is compared with the specific reference patterns prepared in advance, thereby recognizing the embossed characters
235
on the card
234
using the pattern matching procedure.
For example, if the embossed characters
235
are a series of the characters “0123” as shown in
FIG. 3
, the area change of these characters
235
along the translation or moving direction A is converted to the change of an electric current as shown in FIG.
4
. This pattern of the electric current is compared with the reference patterns to thereby recognize the characters
235
through the pattern matching procedure. Thus, the characters
235
are found “0123”.
With the conventional optical conductive-pattern recognition apparatus shown in
FIG. 1
, however, there is the following problem
Specifically, the conductive pattern
110
of the PWB
109
is typically made of copper (Cu) and the insulator
133
of the PWB
109
is made of an epoxy resin reinforced by a glass cloth. Therefore, the conductive pattern
110
has metallic luster allowing the illuminated light to be efficiently reflected. On the other hand, the insulator
133
having a rough surface causes irregular reflection and/or transmission of the illuminated light, resulting in reduction of reflection of the illuminated light.
Moreover, the conductive pattern
110
made of copper tends to be oxidized by salts or acids adhered on human hands and oxygen (O
2
) contained in the atmospheric air, thereby forming a thin film of copper oxide on the pattern
110
. The thin film of copper oxide thus produced is difficult to reflect the illuminated light. As a result, the obtainable intensity difference of the light between the conductive pattern
110
and the insulator
133
becomes small and consequently, recognition error tends to occur.
There arises a similar problem when the conductive pattern
110
is made of a dark-colored material such as carbon paste or a conductor/resin mixture such as conductive paste. If things come to the worst, recognition of the pattern
110
will become impossible.
With the conventional pressure-sensitive conductive-pattern recognition apparatus shown in
FIG. 2
, there is a problem that the embossed characters
235
is unable to be recognized unless the characters
235
are protruded from their neighboring area. This is because the reading or recognition operation is performed by detecting the change of the electric resistance of the pressure-sensitive rubber roller
236
.
Also, there is another problem that recognition is possible for simple patterns only due to the following reason.
It is popular that the conductive patterns of PWBs are complex compared with the embossed characters
235
. Therefore, the change of the electric resistance obtained from the conductive patterns of PWBs is difficult to be pattern-matched with the reference patterns. Further, the reference patterns themselves are extremely difficult to be prepared in advance.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a conductive-pattern recognition apparatus that recognizes a conductive pattern accurately independent of the material and the surface state of the conductive pattern.
Another object of the present invention is to provide a conductive-pattern recognition apparatus that prevents recognition errors even for complex conductive patterns.
Still another object of the present invention is to provide a conductive-pattern recognition apparatus that recognizes a conductive pattern depressed from or leveled with its neighborhood as well as a conductive pattern protruding from its neighborhood.
The above objects together with others not specifically mentioned will become clear to those skilled in the art from the following description.
A conductive-pattern recognition apparatus according to a first aspect of the present invention is compris
Kerveros James C
Metjahic Safet
NEC Corporation
Sughrue Mion Zinn Macpeak & Seas, PLLC
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